1.   Investigators say nuts were missing from a key bolt in the track-switching points at Potters Bar, causing a track to fracture under the added stress.

2.   Investigators say nuts were missing from key bolts in the points structure, causing a track to fracture under the added stress.

3.   Afterwards two sets of nuts from key bolts in the points structure were discovered lying on the ground by the track.

4.   John Armitt, the chief executive of rail operator Railtrack, said nuts were missing from key bolts in the points structure.

5.   Nuts were missing from key bolts in the structure, and the high-speed train passing over put undue pressure on a track, causing it to fracture.